The present invention relates to a thermally developable material which forms images employing thermal development, and a thermally developable material which exhibits high sensitivity as well as minimal fog, and improved pre-exposure storage stability, as well as a method for producing the same.
The present invention relates to a thermally developable photosensitive material, and particularly to a thermally developable photosensitive material which results in no layer peeling during thermal development and exhibits excellent heat resistant dimensional stability.
Heretofore, a number of investigations have been performed on thermal development processes in which the development process is thermally carried out, and those which provide black-and-white images as well as color images, have been known. Further, a so-called thermal transfer type thermally developable material (hereinafter occasionally referred to as photosensitive material), in which an image obtained by thermal development is transferred from a photosensitive material to an image receptive layer, is also well known. A photosensitive material employing such a thermal development system is prepared by directly coating a prepared composition, as descried below, onto a film support. Said composition is prepared by adding a solution prepared by dissolving a reducing agent and a binder comprised of a thermoplastic resin in an organic solvent to an organic solvent dispersion comprising organic silver salts and silver halides. However, when the thermally developable photosensitive material, which is prepared as described above, is actually developed at a temperature of 80 to 150xc2x0 C., practical problems have occurred in which the layer peels off due to thermal contraction of the support and the binder, and the decrease in the elastic modulus.
In order to minimize the layer peeling of a thermally developable photosensitive material during thermal development, it is generally known that a film support and a binder, which are commonly comprised of a thermoplastic resin having a glass transition point higher than the thermal development temperature, is employed. By employing a film support comprised of a thermoplastic resin and a thermoplastic binder having a glass transition point higher than the thermal development temperature, thermal contraction (deformation) as well as a decrease of elastic modulus due to heat is minimized to prevent the undesired layer peeling. However, it was found that even though the thermoplastic resin, having a glass transition point higher than the thermal development temperature, is employed, said layer peeling occurred.
Conventionally, in many thermally developable materials, the image forming layer, and the like, have been formed by applying a coating composition, in which organic solvents such as methyl ethyl ketone, methanol, and the like are employed. These solvents are highly soluble in water. As a result, during the production of a coating composition, water due to moisture condensation is inevitably introduced into the coating composition. Furthermore, organic silver salts comprise moisture depending on drying. In addition, it is difficult to sufficiently dry a thermally developable material at a high temperature after coating. Currently, in the thermally developable material after drying, there remains not only moisture but also organic solvents. Then, the following facts were discovered. Silver ions are dissociated from organic silver salts, such as silver behenate and the like, in the presence of moisture which is diffused to an image forming layer from the support and remains in the coating composition. Therefore, the resulting ions promote reactions of the organic silver salts with the reducing agents incorporated into the thermally developable material, and the formation of such silver ions is one of the big causes which result in fogging during production, as well as during pre-exposure storage.
In view of the foregoing, an object of the present invention is to provide a thermally developable photosensitive material which results in no layer peeling during thermal development, exhibits excellent heat resistant dimensional stability, and minimizes variation in dimensions due to heat. Another object of the present invention is provide a thermally developable material which exhibits high sensitivity as well as minimal fog, and excellent pre-exposure storage stability.
The present inventors have diligently investigated means to solve the problems described above, and have discovered that moisture as well as remaining solvents in a film support and a binder work as a plasticizer during thermal development, and results in thermal contraction (deformation) of the film support as well as of the binder, and also results in a decrease in the elastic modulus due to heat which in turn causes layer peeling. Thus it has been discovered that by controlling the moisture content ratio and/or the remaining solvent content ratio in a thermally developable photosensitive material, and the moisture content ratio of the film support, as well as a coating composition in a thermally developable photosensitive material which is prepared by coating a coating composition comprising organic solvents onto a film support, so that a thermally developable photosensitive material is obtained which results in no layer peeling during thermal development, exhibits excellent heat resistant dimensional stability, and minimizes variation in dimensions due to heat. Thus the present invention is accomplished. Further, the amount of the aforementioned moisture and remaining solvents correlates to fog formation during pre-exposure storage. By controlling said amount, it is possible to control the fog formation during pre-exposure storage. Thus, it was further discovered that it is possible to obtain a thermally developable photosensitive material which minimizes variation in dimensions due to heat.
Namely, the aforementioned objects of the present invention are achieved employing the embodiments described below.
The thermally developable photosensitive material of the invention comprises a layer containing organic silver salt, photosensitive silver halide and reducing agent provided on a support. Moisture content ratio of the support is not more than 0.5 percent by weight.
The moisture content ratio of the thermally developable photosensitive material after storage for 3 hours at 23xc2x0 C. and 55% RH is preferably 0.5 percent by weight.
The moisture content ratio of the support is preferably 0.01 to 0.5 percent by weight.
The layer preferably contains a binder in an amount of 1.5 to 10 mg/m2.
The layer is preferably composed of coating composition containing organic silver salt, photosensitive silver halide and reducing agent and having moisture content ratio of 2 weight % or less.
The average grain diameter of the organic silver salt is preferably 1 xcexcm or less.
The aspect ratio of the organic silver salt is preferably at least 3.
The total amount of silver halide and organic silver salt is preferably 0.5 to 2.2 g per m2 in terms of silver amount.
Preferable example of the reducing agent is a compound represented by formula 
wherein R represents a hydrogen atom or an alkyl group having from 1 to 10 carbon, and Rxe2x80x2 and Rxe2x80x3 each represents an alkyl group having from 1 to 5 carbon.
The amount of the reducing agent is preferably 1xc3x9710xe2x88x922 to 10 moles per mole of silver.
The preferable example of the organic silver is silver behenate or silver arachidinate.
The coating composition is preferably coated on the support whose moisture content ratio is adjusted immediately before the coating not more than 0.5 percent by weight.
The amount of organic solvent is preferably 2.0 percent by weight or less.
The support is preferably subjected to discharge treatment.